Cells are continually challenged on a daily basis, resulting in multiple lesions forming in DNA. The lesions, if not repaired, can lead to mutations or cell death, thus complex signalling networks exist which ensure that lesions are detected, and repaired to maintain the integrity of DNA.
Detection of DNA damage initiates a series of events which are key in maintaining the genome. Cell cycle checkpoints are designed to stop the cell cycle and allow repair of the lesion before allowing the cell to continue into mitosis.
Two key checkpoints have been identified, one at the end of G1 phase and the second at G2, which work in tandem to ensure all lesions, are identified and repaired. In 50% of human cancers the G1 checkpoint is non-functional due to mutations in the tumour suppressor gene p53. However, the G2 check-point is seldomly mutated, and often found to be activated in cancer cells. Cancer cells exploit this to confer resistance to treatment modalities including DNA damaging agents and radiation.
Three kinases have been identified as key regulators of the G2 checkpoint, namely Chk1, Chk2 and Wee-1. Inhibitors for the kinases are currently in clinical trials.
Wee-1 is a nuclear tyrosine kinase, which negatively regulates entry into mitosis, at the G2/M check-point by catalysing a phosphorylation of the cdc2/cyclin B kinase complex. The phosphorylation occurs on the Tyrosine 15 residue and leads to the inactivation of cdc2/cyclin B complex ultimately preventing mitosis. Wee-1 function is intimately linked to that of Chk1 and Chk2 due to their phosphorylation and inactivation of cdc25 on serine 216, as well as the reported activation of Wee-1 by Chk 1 & 2 (Ashwell et al., 2012, DNA Repair in Cancer Therapy, DOI: 10.1016/B978-0-12-384999-1.10010-1).
Wee-1 is downstream of the Chk family and is a crucial component of the checkpoint signalling cascade as it prevents cells from entering mitosis if lesions are detected.
Commonly administered anti-cancer compounds induce DNA damage; including anti-metabolites, platiniums, topoisomerase inhibitors and alkylating agents. However, their efficacy is limited due to excessive toxicity, resistance and lack of tumour selectivity. Compounds which work in combination with these agents to prevent DNA repair selectively in tumour cells would be extremely beneficial. The tumour suppressor gene p53 is commonly mutated in tumour cell lines, therefore the administration of a Wee-1 kinase inhibitor, which will abrogate the G2 check point, may lead to increased sensitivity to DNA damaging agents. The potential for this has been reported, silencing of Wee-1 activity was sufficient to sensitize HeLa cells to doxorubicin due to abrogation of G2 arrest. In contrast, in normal breast epithelium which have a fully complement p53, the removal of Wee-1 function had little additional effect compared to doxorubicin alone (Wang et al., 2004, Cancer Biology and Therapy, 3(3), 305-313).
It has been reported that cell lines harbouring mutations in the tumour suppressor gene p53 have increased sensitivity to DNA damaging agents when co-administered with Wee-1 small molecule inhibitors. In vitro and in vivo efficacy has been reported when small molecule inhibitors are combined with gemcitabine, 5-fluorouracil, carboplatin, cisplatin (Hirai et al 2010, Cancer Biology & Therapy 9:7, 514-522), cytarabine (Tibes et al., 2012, Blood, 119(12), 2863-2872) and Src inhibitors (Cozzi et al., 2012, Cell Cycle 11(5), 1-11). Single agent apoptotic efficacy, independent of p53 status, has been reported in sarcoma cell lines and in patient derived sarcoma samples (Kreahling et al., 2012, Mol. Cancer Ther., 11(1), 174-182).
Irradiation is known to increase phosphorylation of the Tyr15 and Thr14 residues of cdc2, leading to a radioresistant phenotype. Inhibition of Wee-1 activity by small molecules (Wang et al., 2004, Cancer Biology and Therapy 3(3), 305-313) leads to a reduction in phosphorylation and radiosensitization effect, with the effect more pronounced in p53 mutant cell lines.
Compounds having a kinase inhibitory effect, for example a Wee-1 kinase inhibitory effect, are described in WO 2007/126122, US 2010/0063024, EP 2,213,673, WO 2008/133866 and US 2007/0254892.
WO 2010/067886, WO 2010/067888, US 2011/0135601, EP 2,168,966, WO 2005/090344, US 2009/0048277 and Bioorg. Med. Chem. Lett., 2005, 15, 1931-1935 describe various compounds such as dihydropyrimidopyrimidine and pyridopyrimidinone derivatives having a kinase inhibitory effect. In particular, the compounds of WO 2005/090344 are said to show activity as protein kinase inhibitors, in particular Src family tyrosine kinase inhibitors. The compounds described in Bioorg. Med. Chem. Lett., 2005, 15, p 1931-1935 are said to be 10-100-fold more potent inhibitors of c-Src than Wee-1, and variation of substituents on the 6-phenyl ring does not markedly alter this preference. It is said that solubilizing substituents off the 2-anilino ring in many cases increases Wee-1 activity, lowering this preference to about 10-fold. 5-Alkyl substituted analogues are said to be generally Wee-1 selective, but at the expense of absolute potency.
WO 2013/013031 describes pyridazino[4,5-d]pyrimidin-(6H)-one inhibitors of Wee-1 kinase which are said to be useful for inhibiting kinases such as Wee-1 and in methods of treating diseases such as cancer. Compounds within the scope of disclosure of WO 2013/013031 have a nitrogen atom at the ‘3-position’ of the ring relative to the carbonyl group.
US 2013/0018045 describes various tricyclic 2-sulfonamide compounds which are useful for inhibiting kinases such as Wee-1 and methods of treating diseases such as cancer. Compounds within the scope of disclosure of US 2013/0018045 have a sulfonamide group at the ‘1-position’ on the ring and the atoms at the ‘3- and ‘4-positions’ form part of a fused aryl or heteroaryl ring (A).
It is one object of the present invention to overcome at least some of the disadvantages of the prior art or to provide a commercially useful alternative thereto.
It is a further object of the present invention to provide a compound having an improved selectivity towards Wee-1 kinase compared to known compounds or compositions.
It is a further object of the present invention to provide a compound having an improved stability in human microsomes, for example human liver microsomes, compared to known compounds or compositions.
It is a further object of the present invention to provide a compound having an enhanced or similar kinase-inhibitory effect compared to known compounds or compositions.
It is a further object of the present invention to provide a compound having an improved efficacy compared to known compounds or compositions.
It is a further object of the present invention to provide a compound having an improved efficacy and tolerability when administered in combination with other therapies compared to known compounds or compositions.
It is a further object of the present invention to provide a compound having an improved tolerability compared to known compounds or compositions.